4. Plaintiff may challenge the propriety of an affirmative defense by motion under Rule 12(f). Before Twombly and Iqbal, an affirmative defense generally was treated as sufficient if it provided notice of the possible existence of the defense and defendant’s intention to advance it, but courts now are divided as to whether defenses are subject to the standard of plausible pleading. Compare Kaufmann v. Prudential Ins. Co. of Am., 2009 WL 2449872, at *1 (D.Mass.2009)(“* * * [T]he court is inclined to think that a defendant has the same Rule 8 obligations * * * as does a plaintiff.”), with Falley v. Friends University, 787 F.Supp.2d 1255, 1258 (D.Kan.2011) (“Applying the Twombly standard * * * would likely result in increased motions practice with little practical impact on the case’s forward progression.”).

See Seiner, PlausibilityBeyond the Complaint, 53 Wm. & Mary L. Rev. 987 (2012).